Abstract
X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder caused by mutations in the ABCD1 gene that encodes the peroxisomal ATP-binding cassette (ABC) transporter subfamily D member 1 protein (ABCD1), which is referred to as the adrenoleukodystrophy protein (ALDP). Induction of the ABCD2 gene, the closest homolog of ABCD1, has been mentioned as a possible therapeutic option for the defective ABCD1 protein in X-ALD. However, little is known about the transcriptional regulation of ABCD2 gene expression. Here, through in silico analysis, we found two putative TCF-4 binding elements between nucleotide positions -360 and -260 of the promoter region of the ABCD2 gene. The transcriptional activity of the ABCD2 promoter was strongly increased by ectopic expression of β-catenin and TCF-4. In addition, mutation of either or both TCF-4 binding elements by site-directed mutagenesis decreased promoter activity. This was further validated by the finding that β-catenin and the promoter of the ABCD2 gene were pulled down with a β-catenin antibody in a chromatin immunoprecipitation assay. Moreover, real-time PCR analysis revealed that β-catenin and TCF-4 increased mRNA levels of ABCD2 in both a hepatocellular carcinoma cell line and primary fibroblasts from an X-ALD patient. Interestingly, we found that the levels of very long chain fatty acids were decreased by ectopic expression of ABCD2-GFP as well as β-catenin and TCF-4. Taken together, our results demonstrate for the first time the direct regulation of ABCD2 by β-catenin and TCF-4.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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ATP Binding Cassette Transporter, Subfamily D
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ATP-Binding Cassette Transporters / genetics*
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Adrenoleukodystrophy / genetics*
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Adrenoleukodystrophy / pathology
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Adrenoleukodystrophy / therapy*
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Base Sequence
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Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / metabolism*
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Binding Sites / genetics
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Fatty Acids / metabolism
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Fibroblasts / metabolism
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Fibroblasts / pathology
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Gene Silencing
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Green Fluorescent Proteins / metabolism
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Hep G2 Cells
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Humans
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Molecular Sequence Data
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Molecular Targeted Therapy*
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Promoter Regions, Genetic / genetics
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Recombinant Fusion Proteins / metabolism
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Transcription Factor 4
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Transcription Factors / metabolism*
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Transcription, Genetic
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Transcriptional Activation / genetics
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Up-Regulation / genetics
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beta Catenin / metabolism*
Substances
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ABCD2 protein, human
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ATP Binding Cassette Transporter, Subfamily D
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ATP-Binding Cassette Transporters
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Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
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Fatty Acids
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RNA, Messenger
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Recombinant Fusion Proteins
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TCF4 protein, human
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Transcription Factor 4
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Transcription Factors
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beta Catenin
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Green Fluorescent Proteins
Grants and funding
This research was supported by grants from the National Research Foundation, Korean Ministry of Education, Science and Technology (the Bio & Medical Technology Development Program, 2012M3A9B4028631 and 2012M3A9C7050126), Korea Health technology R&D Project, Korean Ministry of Health & Welfare (A120254 and A100694). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.